An automatic standby current shutoff

[saunj]

I measured the current drawn by the several units of my entertainment center and discovered that the total was 35 watts even when all were off. The main culprit is the "Set-Top Box" which I am obliged to rent from my cable company. This unit draws full power even in its "Bypass" setting, and has no power control. I think its manufacturer, Scientific Atlanta, should be required to purchase "Carbon Credits" for its environmentally-irresponsible design.
This device cuts off the power to all with a relay when all units go on standby. Their remote controls turns it back on.
To save money, I made this device around a surplus "Coffee Timer", available as item 16742 MI from MPJA for $3.99. This provides a power supply (with only 1 watt draw when the relay is off), 10-amp relay, and a relay driver transistor. And, of course, a clock. The timer function is disconnected, but the control knob with AUTO-OFF-ON selection retains these same functions. In AUTO mode the picaxe 08M-powered electronics senses an IR-remote sensor and a current-measuring shunt resistor with isolating transformer. Any remote button press on any of the several entertainment-center remotes will activate the relay, which will be kept on by the resulting current draw, and for 20 minutes after all units are put on standby.
In normal conditions, this device needs no attention.
I have posted more information in my web site here:
http://www.worsleyassociates.com/Projects/Power_Saver/index.html?

 

[fernando_g]

saunj:
You have peered into the dark recesses of the "power vampires". Indeed, as you have discovered, many household electronic devices consume substantial power when they are "off". There is plenty of info on this topic over the web.

The worst offenders, by far, were the old "instant-on" CRT-equipped TVs. The CRT is a vacuum tube after all, and to have an instant-on feature, its heater remained energized 24/7.

This led to programs like Energy-Star and TCO certification, which mandated on its first implementation a standby current of less than 5 watts, but in its subsequent revision it has come to less than 1/2 watt.

Now to your circuit...I like the fact that you employed comercially available gadgets like the coffee timer as the user interface.
Additionally, the use of a shunt resistor/voltage transformer to sense current is very clever.